1. Field of the Invention
This invention relates to a butterfly valve to prevent dew condensation therefrom, and more particularly relates to a butterfly valve which prevents dew condensation from producing on its external surface resulting from the temperature difference between the atmosphere and fluid which flows in a pipe.
2. The Related Art
In the prior art pipes in which low temperature fluid flows, such as air conditioning, steps are taken to cover the external surface with an insulating material for preventing dew condensation. Without insulation, dew condensation from the moisture in the atmosphere is produced on the external surface of butterfly valves and pipes by the temperature difference between flowing fluid and atmosphere.
An insulating material can cover a part of a shaft cylinder including a valve body. However, it is difficult to cover all of a shaft cylinder which extends at right angles to a pipe line and an actuator, etc., connected to the shaft cylinder, because those shapes are very complicated and have a different direction from the piping line.
In the prior art, such parts are exposed to the atmosphere and it is a problem that dew condensation from the moisture of the atmosphere occurs on the external surface of a shaft cylinder and actuator which are exposed to the atmosphere. Also, corrosion occurs by water drops from dew condensation and the floor becomes dirty by water dropping from the valve.
Therefore, attempts have been made to cover said shaft cylinder and actuator. However, it is difficult to apply many kinds of insulating material to one butterfly valve because a separate insulating cover which is different from one covering a piping line is necessary, because of the location of shaft cylinder and actuator is at right angles to a piping line, and because an actuator has a very complicated external surface shape. Actuators also have different shapes and structure in accordance with the function, use, place for use and controlling system, etc.
For example, in the typical prior art, as shown in FIG. 26, the butterfly valve (1) is attached between pipes (2)(2) and/or flanges (3)(3).
Even though the valve body of butterfly valve (1) and pipes (2)(2) are covered by insulating material, a shaft cylinder which extends to the direction at the right angles to pipes (2)(2) and actuator (7) cannot be covered by the same insulating cover (5) as covered by the external surface of said valve body. Therefore, a separate insulating cover is prepared and covers a shaft cylinder (6) and actuator (7).
This separated insulating cover must be prepared for each valve in accordance with the shape and structure of actuator. The use of this separate insulating cover requires locating an open indicator (9) at the outside of the cover (8) because the indicator must be read.